TH‐C‐217BCD‐03: Evaluation of the Spatial Resolution and Noise Properties of a Prototype Transmission Ultrasound Imaging System Employing an Acousto‐Optic (AO) Detector

Abstract

Purpose: In this work, the spatial resolution and noise properties of a prototype full‐field transmission ultrasound imaging system employing an acousto‐optic (AO) liquid crystal detector were characterized. The AO effect is a phenomenon in which an incident acoustic wave field induces local birefringence changes in a liquid crystal. These birefringence changes manifest as brightness changes when the liquid crystal is optically illuminated using polarized light, thus providing spatial information about the field. Methods: A compressed, Zerdine‐based breast phantom containing 12 artificial spherical lesions was imaged using plane‐wave ultrasound illumination. Lesions of diameter 2 mm, 4 mm, 6 mm, and 8 mm were embedded at depths of 12.7 mm, 25.4 mm, and 38.1 mm within the phantom background. To minimize coherence artifacts, the transducer frequency was swept continuously from 3.25 MHz to 3.45 MHz at a rate of 100 MHz/s. The transducer voltage was ramped from 0.1 V to 6.5 V to permit identification of the onset of the AO effect in the detector. An analysis of image quality was performed on 50 identically acquired images in which the contrast‐to‐noise ratio was determined for each lesion in the mean acquired image. Apparent lesion size was also computed as a function of distance from the AO detector. Results: The spatial resolution analysis revealed that lesion size in the mean acquired image increased linearly with lesion‐to‐detector distance. Extrapolation of the least squares regression lines for apparent lesion size versus lesion‐to‐detector distance to zero distance agreed well with the actual lesion sizes. The noise analysis demonstrated that a contrast‐to‐noise ratio of 13.1 could be obtained with the prototype system for the transducer settings and phantom properties considered. Conclusions: This investigation indicates the potential for incorporating a liquid crystal AO detector into a transmission ultrasound system for full‐field breast imaging.